Trees absorb nutrients from the soil through their root systems.
When potted, repeated watering can quickly wash these nutrients away.
A bonsai tree requires consistent feeding with a fertilizer mix to replenish the nutritional content of its soil.
Plants require water and sunlight, along with carbon, hydrogen, and oxygen from the air to create the sugars they need to grow.
They also require specific nutrients from the soil to be able to produce amino acids, vitamins, proteins, and enzymes.
Most plant soils naturally have a mix of these nutrients, but some, even those called "bonsai soils" such as Japanese clay, can be lacking.
The three most important components of a balanced fertilizer are nitrogen, phosphorus, and potassium.
Bonsai food must contain a balanced mixture of these ingredients.
Nitrogen is responsible for the size and amount of leaf and stem growth.
It is also necessary for cell division, the manufacturing of protein and, even to some extent, the leaves' green color.
Phosphorus helps to stimulate cell division and encourages healthy root growth and bud development.
Additionally, it protects against disease.
Finally, potassium (usually in the form of potash for plants) helps flower and fruit production and also fights disease.
When you're shopping for bonsai food, you don't have to look for a special bonsai mix, but you do want fertilizer that is labeled N-P-K (K is potassium) in equal amounts such as 10-10-10, or 20-20-20, so you know it contains these essential elements.
When in doubt about which fertilizer is right for your bonsai species, ask an expert at the nursery.
There are different ways to apply fertilizer.
One option is to use solid pellets or small cakes of fishmeal or rapeseed.
These are slow-release nutrient mixes, meaning you only have to feed your bonsai every few weeks, but they can encourage pests and are not pleasant looking.
Most bonsai enthusiasts use soluble powders or liquid food applied to damp soil every other week or so or as directed on the fertilizer package.
Most bonsai should be fed throughout the early spring and summer during their regular growing season.
When growth slows down in the autumn it is harder for them to absorb nutrients, so trees will only need feeding once a month.
When deciduous trees lose all their leaves, you can stop feeding until spring; conifers will only need a few feedings over the winter.
Tropical indoor bonsai trees can be fertilized all year round.
It's important to remember not to feed a tree immediately after repotting as this can damage the roots.
The tree will need to be simply watered for at least a month before resuming feeding.
Always water your bonsai before fertilizing, and be careful not to overfeed.
It is better to underfeed than to overfeed; if the nitrogen content of the compost in the pot becomes too high it will burn the roots.
This will result in less growth, not more! Also, never feed a dormant or sick tree, as too many nutrients in the soil will cause problems.